Murine Plasmocytomas grown in tissue culture will be used as a model system to analyze the controls on gene expression in mammalian cells. Plasmocytoma, MOPC315, synthesizes and secretes large amounts of a specific immunoglobulin (IgA, lambda). Mutants and variants that fail to synthesize immunoglobulin will be isolated and characterized. Mutants, variants, and revertants will be subjected to complementation analysis in vitro and in vivo to assess dominance relationships and to define separable functions. In vitro complementation will be done by employing a cell-free system capable of synthesizing immunoglobulin. In addition, biochemical characterization of the cells of interest will be done such that defects or alterations in transcription, RNA processing and transport, and translation can be detected. We should be able to describe those functions that are essential for expression of a differentiation program. This study should provide invaluable information on the process of neoplastic transformation regardless of its etiology. In addition to the study of general aspects of gene expression, we will analyze the genetic potential in these cells with respect to immunoglobulin synthesis. Mutants, variants, and revertants will be sought that alter the nature of the immunoglobulin synthesized. We will endeavor to isolate cells that differ from the parental line in that their expressed immunoglobulin has an altered structure (constant or variable regions). These studies will allow us to gain insight into the mechanics of the immune system and aid in our understanding of the immunological defense against disease.